Heat exchangers are traditionally used to heat or cool potable or process critical fluids using non-potable fluids while providing a physical, mechanical boundary to prevent contact between the respective fluid streams.
Heat exchangers, as with all mechanical devices, have finite operating timeframes at the end of which the devices fail for one or more reasons. One typical failure mode for heat exchangers is an external leak in which one or both fluids escape to the outside environment or atmosphere. Another typical failure mode for heat exchangers is an internal leak in which one or both fluids mix with one another without escaping to the outside environment. Internal leaks are not observable from the exterior of the heat exchanger, whereas external leaks may be visually evident.
To avoid an internal leak, which may not be readily observed by an operator of a single-wall heat exchanger, it is desirable to provide a vented, double-wall boundary that exhausts the leaking fluid to the outside environment or atmosphere in lieu of having the respective fluids mix inside the heat exchanger while the heat exchanger continues to operate. A double-wall heat exchanger is one in which the boundary separating the two fluids is comprised of two separate surface layers, rather than one. Thus, if the first surface layer fails to provide a fluid tight barrier, the second layer should remain intact, causing the leaking fluid to flow between the surface layers to a location where the leaking fluid can be detected externally of the heat exchanger. The double-wall construction is intended to be a safety feature to prevent cross-contamination of the fluids. A double-wall heat exchanger is disclosed for example, in U.S. Patent Application Publication No. 2007/0169916 to Wand, which is incorporated by reference herein in its entirety.
The double-wall heat exchanger disclosed in Pub. '916 to Wand is vented, i.e., it includes an aperture that channels internal leaks to an exterior surface of the heat exchanger. The aperture is defined on the boundary edge of the heat exchanger. Any leakage that forms on the boundary edge of the heat exchanger may be difficult to observe. In view of the foregoing, it is preferable to direct the leaking fluid to a location on the heat exchanger where the leaking fluid can be readily detected so that the faulty heat exchanger can be removed from service.